Line protector for a communications circuit

ABSTRACT

A line protector for a communications circuit provides overvoltage and overcurrent protection. The overvoltage protection is attained through an arrester that provides an arc gap from the line to ground. For overcurrent protection, a fusible element is melted by a heat coil causing the line to be directly grounded. A test terminal is in conductive connection with the line circuit and extends to a region in the housing wall wherein there is an aperture for receiving a test probe. The test terminal is in firm resilient engagement with a conductive component of the line circuit and the wall adjacent to the apertures whereby the test terminal is maintained in its desired position within the housing to avoid short circuits therein.

BACKGROUND OF THE INVENTION

This invention relates to improvements in communications lineprotectors, and more particularly to line protectors of the type thatare located between central office switching equipment and insideswitching-related equipment. The purpose of these line protectors is toprotect the inside equipment from damage as a result of overvoltage andovercurrent conditions on the outside lines. One such line protector isshown in U.S. Pat. No. 4,168,515 issued Sept. 18, 1979, and the presentinvention is an improvement that is specifically directed to that lineprotector.

In telephone central offices where these protectors are located, theyare typically mounted on a protector panel or connector board and withthe protector devices being inserted into contacts on the board. Theconnector board is generally located at the juncture between outsideplant lines and the central office equipment. Each protector unitgenerally serves the purpose of protecting both the tip side and thering side of each line pair which are terminated on the connector panel.Generally speaking, the panel incorporates a test field so thatelectrical tests may be made on outside facilities or inside equipmentin a convenient manner. Where a test field is not used or embodied onthe connector panel, access for testing of the telephone pairs for eachmodule may be conveniently accomplished by access holes in the modulehousing so that probes may be inserted into the housing for contact withthe tip and ring circuits therein. One such arrangement is shown in U.S.Pat. No. 4,307,430 that issued Dec. 22, 1981. Rather than incorporatingthe features of U.S. Pat. No. 4,307,430, the present invention involvesthe novel modification of an existing commercial form of line protectoras shown in U.S. Pat. No. 4,168,515, referred to above.

SUMMARY OF THE INVENTION

An object of this invention is to provide a line protector of thecentral office type having facilities for line testing through testterminals within the module and to which access may be had by testprobes through apertures in the wall of the module housing.

A more specific object of this invention is to provide a line protectorof the type stated in which the test terminal is resilient and is bentwithin its elastic limits to maintain its position within the module andalso to provide intimate contact with its associated line circuit in themodule.

Broadly speaking, the invention comprises a line protector for acommunications circuit comprising a housing having an end wall and anopening opposite to said end wall, an insulating member forming a baseclosing said opening, conductive line pins and a ground pin projectingfrom said base, a first conductive element secured to one of said linepins and a second conductive element secured to the other line pin, eachconductive element and its associated pin being electrically insulatedfrom the other conductive element and its associated pin, a heat coilassembly having portions secured together by a fusible substance, a coilof wire having one end connected to one conductive element and the otherend of the coil connected to the other conductive element, thereby toform a protector circuit between the line pins and wherein the coilgenerates heat to melt the fusible substance upon an overcurrentcondition in a communications line circuit in which the protectorcircuit is a part, a surge voltage arrester in a normally open circuitfrom said line circuit to said ground pin, a conductive test terminal insaid housing, said test terminal extending between said end wall and oneof said conductive elements, said test terminal being resilient andhaving a normal length that is greater than the distance between saidend wall and said one conductive element so that said test terminal isbent within its elastic limits to maintain intimate contact at one endwith said one conductive element and at its other end with said endwall, and said end wall having an aperture at which said test terminalis exposed for receiving a test probe to test said line circuit, andmeans including the resiliency of said test terminal and cooperatingportions of said housing and said terminal to aid in maintaining saidtest terminal in a fixed position in said housing.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a front elevational view, partially in section;

FIG. 2 is a side elevational view, partially in section;

FIG. 3 is a top plan view of the module of FIGS. 1 and 2; and

FIG. 4 is an enlarged fragmentary sectional view taken along line 4--4of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMB0DIMENT

Referring now in more detail to the drawing, there is shown a protector2 having a generally rectilinear insulating plastic housing 4. One endof the housing 4 has an end wall 6 which merges into a neck 8 and aflange 10 by which the protector may be gripped for removal from andplacement into a plug-in type of terminal board having wired connectionsto the incoming outside lines and also to the inside or central officeequipment. The end wall 6 has a pair of perforations or apertures 12, 14for test probe access as will presently be more fully described. At itsend opposite to the wall 6 the housing is open, and this opening isclosed off by a plastic base 13 containing laterally projecting lockingtabs 15. These tabs 15 interlock with a snap fit into openings 17adjacent to the resilient open end of the housing.

Projecting through the base 13 are conductive plug-in terminal pins 16,18, 20, 22 and 24. More specifically, there is a first line pin 16, ashorter first central office pin 18, a second line pin 20, a shortersecond central office pin 22, and a ground pin 24. The line pin 16 andcentral office pin 18 are in one of the incoming line pairs (tip orring) through the protector while the second line pin 20 and itsassociated central office pin 22 are in the other line circuit throughthe protector. The ground pin 24 is suitably connected through theplug-in receptacle to ground in a conventional manner.

In the line circuit between the pins 16, 18 there is a heat coil circuit26, and likewise in the line circuit of the pins 20, 22 there is a heatcoil circuit 28. These heat coil circuits are of similar construction,and therefore, only one circuit need be described with like referencenumerals being applied to both heat coil circuits 26, 28. Each heat coilcircuit is characterized by the fact that there are permanentconnections from one line pin to the other line pin. For example, thereis a permanent connection between line pins 16 and 18 and through heatcoil circuit 26. These connections are preferably brought about bystaking the line pin to respective contact plates (hereinafterdescribed) and by welding the ends of the heat coil wire to therespective contact plates.

A sub-base 30 of insulating plastic is of generally rectilinearconfiguration but includes a lower step or surface 32 and an upper stepor surface 34. The lower step 32 receives a metallic contact plate 36which is of generally U-shaped cross section as seen in FIG. 1. Theplate 36 has a hole 37 for receiving the upper end of the pin 22 whichis upset or staked into rigid and permanent mechanical and electricalcontact with the plate 36. The hole 37 and the plate 36 is aligned witha hole 38 in the sub-base 30 for receiving a section of the pin 22.

A second contact plate 40, also of U-shaped cross section, is mounted onthe upper step 34. The plate 40 overhangs or projects beyond the uppestep 34 so as to lie spaced above the plate 36. The overhang part of theplate 40 has a slot 42 for purposes presently more fully appearing. Theupper end of the line pin 20 projects through the plate 40 and is upsetor staked in place to provide a rigid and permanent mechanical andelectrical connection therewith. The line pin 20 also projects through ahole 44 in the sub-base 30 such that the two pins 20, 22 are in parallelrelationship. The pins 20, 22 also freely pass through holes 21, 23 inthe base 10.

The upper step 34 has an upwardly and laterally opening cavity 46 foraccommodating the reduced diameter lower end of a heat coil pin 48. Thiscavity 46 may extend into or merge with the hole 44. The heat coil pin48 projects perpendicularly from the plate 40, and the heat coil pintelescopes within a tubular metallic member constituting a heat coilbobbin 50 having a flanged end 52. The heat coil pin 48 and its bobbin50 are normally maintained in a rigid assembled relationship by lowmelting point solder 54 between the pin and the bobbin. The heat coilwire 56 is wound around the exterior of the bobbin 50 and is retained bythe end flange 52. One of the leads 58, 60 from the heat coil passesthrough the slot 42 and those leads are rigidly joined in mechanical andelectrical connection to the respective plates 36, 40.

Also mounted within the housing 4 and associated with the line circuitrunning from the pin 16 to the pin 18 is an overvoltage arrester unit 62of known construction. A like arrester unit 62a is associated with theline circuit running from the pin 20 to the pin 22. The arrester may bea carbon air gap arrester or a cold cathode gas tube. In the embodimentof the invention illustrated, there is a carbon air gap arrester. Thisarrester comprises a carbon rod electrode 64, the lower end of whichabuts the upper end of the heat coil bobbin 50, thus providing anelectrical connection to the associated line circuit. The arrester unit62 also includes a ceramic insulator 66 to which the carbon rod 64 isbonded. Cooperating with the carbon rod electrode is a carbon discelectrode 68 of known construction and which seats against the upper endface of the insulator 66. The end of the carbon rod that faces the disc68 is recessed into the insulator so as to define an arc gap 70.

Each overvoltage arrester unit is housed within an inverted metallic cup72 which also receives the associated heat coil bobbin 50. The loweropen end 74 of the cup 72 is spaced from the plate 40 a distance whichis less than the distance from the upper end of the bobbin pin 48 to thelower end of the carbon rod 64.

Interposed between the end wall 76 of the cup 72 is a volute spring 78.This volute spring 78 applies pressure to the cup 72 which in turnpresses the carbon rod electrode against the bobbin 50. However, thebobbin stays fixed relative to the pin 48 so long as the fusible soldermaterial 54 remains solid.

The upper end of the volute spring 78 presses against a grounding plate80 which is positioned against a boss 79 that projects inwardly from theend wall 6 of the housing. The grounding plate 80 is of such extent thatit contacts both volute springs 78, 78 in the module. This groundingplate is metallic and is staked or otherwise rigidly secured to theground pin 24. The ground pin 24 runs downwardly between the assembliesin each half of the housing so as to project through the base 10. Theextreme end of the ground pin 24 projects into a small cavity 81 in theboss 79.

In a transient overvoltage condition on one of the lines, for examplethe line in which the pins 16, 18 are located, this transient voltagewill be applied through plate 40, heat coil pin 48 and bobbin 50 to thecarbon electrode 64. This voltage will result in an arc across the arcgap 70, through the cup 72, the volute spring 78 and ground plate 80 tothe ground pin 24. Generally speaking, the unit is self-restoring undersuch conditions.

In an overcurrent condition on the same line circuit, the heat coil 56will generate sufficient heat to melt the solder 54. Pressure from thevolute spring transmitted to the carbon rod 64 will press against thebobbin 50 causing it to slide downwardly along the pin 48. The action ofthe spring will move the metallic cup 72 until its end 74 engages theplate 40 to ground the line through the ground pin 22.

Also within the housing are test terminals 84, 86 which are formed ofsheet metal and which extend generally longitudinally of the housing 4.Each test terminal 84, 86 has a small end flange 88 that fits flushagainst the surface of the plate 40. At its end adjacent to the housingwall 6, each test terminal has a large flange 90 which is roughlysemi-circular in shape and which lies in close proximity to theassociated housing aperture 12 or 14, as the case may be. Each topflange 90 has a generally straight edge 92 which fits flush against arelatively flat surface portion 94 on the boss 79, thereby assisting andorienting the test terminals within the housing and aiding in keepingthe test terminals in their desired positions. As a result of the closeproximity of the flanges 90 with the apertures 12, 14, a test probe maybe readily inserted through the apertures 12, 14 for contact with thetest terminals to test the condition of the lines.

The normal or nominal length of each test terminal between its flanges88, 90 is preferably greater than the distance between the insidesurface of the wall 6 and the associated plate 40. Each test terminal isresilient so that the test terminal is bent within its elastic limitsresulting in its length being foreshortened somewhat but with thisresiliency or elasticity of the test terminal being utilized to maintainit in intimate contact with both the wall 6 and the plate 40.Consequently, the test terminals are held in their desired positionsremote from other live parts in the module and preferably such that theparts of the test terminals between the flanges 88, 90 are near thecorners of the module housing.

I claim:
 1. A line protector for a communications circuit comprising ahousing having an end wall and an opening opposite to said end wall, aninsulating member forming a base and having step surfaces, said baseclosing said opening, conductive line pins projecting from said base, afirst conductive element rigidly secured to one of said line pins and asecond conductive element rigidly secured to the other line pin, saidconductive elements being respectively supported by the step surfacesand each conductive element and its associated pin being electricallyinsulated from the other conductive element and its associated pin, aheat coil assembly having telescoping portions rigidly secured togetherby a fusible substance, a coil of wire surrounding said telescopingportions and having one end of the coil connected to one conductiveelement and the other end of the coil connected to the other conductiveelement, thereby to form a protector circuit between the line pins andwherein the coil generates heat to melt the fusible substance upon anovercurrent condition in a communications line circuit in which theprotector circuit is a part, one of said telescoping portions beingrigidly secured to one of said conductive elements, the conductiveelements being between the heat coil and the insulating member, aconductive test terminal in said housing, said test terminal extendingbetween said end wall and one of said conductive elements, said testterminal being resilient and having a normal length that is greater thanthe distance between said end wall and said one conductive element sothat said test terminal is bent within its elastic limits to a conditionforeshortened from its normal length to maintain intimate pressurecontact with said one conductive element and with said end wall, andsaid end wall having an aperture at which said test terminal is exposedfor receiving a test probe to test said line circuit.
 2. A lineprotector according to claim 1 in which said end wall has an inwardlyprojecting boss having a surface that abuts an edge on said testterminal to aid in orienting said test terminal in said housing, saidhousing interior having a generally rectangular cross-section and saidtest terminal, between said end wall and said conductive element,running substantially along a corner of the housing.
 3. A line protectorfor a communications circuit comprising a housing having an end wall andan opening opposite to said end wall, an insulating member forming abase closing said opening, conductive line pins and a ground pinprojecting from said base, a first conductive element secured to one ofsaid line pins and a second conductive element secured to the other linepin, each conductive element and its associated pin being electricallyinsulated from the other conductive element and its associated pin, aheat coil assembly having portions secured together by a fusiblesubstance, a coil of wire having one end connected to one conductiveelement and the other end of the coil connected to the other conductiveelement, thereby to form a protector circuit between the line pins andwherein the coil generates heat to melt the fusible substance upon anovercurrent condition in a communications line circuit in which theprotector circuit is a part, a surge voltage arrester in a normally opencircuit from said line circuit to said ground pin, a conductive testterminal in said housing, said test terminal extending between said endwall and one of said conductive elements, said test terminal beingresilient and having a normal length that is greater than the distancebetween said end wall and said one conductive element so that said testterminal is bent within its elastic limits to a condition foreshortenedfrom its normal length to maintain intimate pressure contact at one endwith said one conductive element and at its other end with said endwall, and said end wall having an aperture at which said test terminalis exposed for receiving a test probe to test said line circuit, andmeans including the resiliency of said test terminal and cooperatingportions of said housing and said terminal to aid in maintaining saidtest terminal in a fixed position in said housing.